Liquid optics with folds lens and imaging apparatus

ABSTRACT

A high performance zoom lens system suitable for use with a camera is disclosed. The zoom lens systems employs redirection of the radiation axis, liquid optics and a movable lens group to provide optical performance over the zoom focal length range at focus distances from close to infinity. The system also provides compensation for undesirable thermally induced effects by adjustments of the zoom group and the variably shaped optical surface in the liquid lens cell.

RELATED APPLICATIONS

This application is related to, and claims the benefit of U.S.Provisional 60/992,244 filed Dec. 4, 2007, the entirety of which ishereby incorporated by reference herein and made a part of the presentspecification.

BACKGROUND

1. Field of the Invention

This invention relates to an optical lens system employing liquid opticsand redirection of a radiation axis.

2. Description of the Related Art

Imaging applications have historically used two or more movable zoomlens groups to provide zooming and different focal lengths. Anadditional lens group for focusing may also be needed.

However, there are intrinsic disadvantages associated in using zoom andfocus lens systems with moving lens groups. In particular, having movingzoom lens groups implies the need for complex mechanically moving parts.Each movable lens group requires support structures and drive mechanicssuch as cams and motors and in some cases control electronics tofacilitate the movements. This system complexity may add size, weightand cost and may make the system operation unreliable over a period oftime. These disadvantages together with undesirable limitations, such asa limited range of focal lengths, the inability to focus adequately overthe entire focal length range, the inability to focus on close objects,the lack of adequate optical performance over the entire focal lengthrange and focus distance, are present in some previously available zoomlenses having at least two moving zoom lens groups. A mechanically lesscomplex but high performance zoom lens system is needed.

SUMMARY

Liquid lens cells comprise two or more fluids in a chamber. The fluidscontact to form a surface that variable by, for example, electricalnodes. A fluid may be, for example, one or more gases, one or moreliquids, or a mixture of one or more solids and one or more liquids.Using liquid lens cells to replace one or more moving lens groupsresults in additional configuration options for the optical path.Replacing moving lens groups with liquid lens cells results in a morecompact system. However, a linear optical design may result in a lensthat is longer than desired. The use of liquid lens cells instead of amoving group facilitates the use of optical elements such as folds toreduce the physical length of a lens. Although the overall length of theoptical path through the lens may remain the same, the liquid lens cellsprovide strategic space for redirection of the radiation axis thatreduces the length in one or more directions. This allows longer overalllens lengths to be used in smaller camera packages. For example, manypoint and shoot cameras and cell phone cameras do not have large amountsof space for a long lens. Using liquid cells in combination with foldsor redirection of the radiation axis allows for better lens systems inthese small camera packages. Larger cameras can also benefit fromreducing the camera package length that would be required for a lenssystem that do not redirect the radiation axis.

It should be understood that the embodiments described herein are forexplanation purposes, and the scope of the invention is not constrainedto the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a camera.

FIG. 2 is an optical diagram of a zoom lens system employing liquids.

FIGS. 3A and 3B are optical diagrams of the liquid cell of the zoom lenssystem of FIG. 2 showing the surface shape between the liquids.

FIGS. 4A, 4B and 4C are optical diagrams of the zoom lens system of FIG.2 illustrating different positions of the zoom lens groups and surfaceshapes between the liquids to produce different focal lengths and focusdistances.

FIGS. 5A, 5B and 5C are modulation transfer function performancediagrams of the zoom lens system of FIGS. 4A, 4B and 4C.

FIG. 6 is an optical diagram of a zoom lens system employing liquids anda single fold.

FIG. 7 is an optical diagram of a zoom lens system employing liquids anda dual fold.

FIGS. 8A and 8B are optical diagrams of a zoom lens system with foldsillustrating different positions of the zoom lens group and surfaceshapes between the liquids.

FIGS. 9A, 9B and 9C are optical diagrams of a zoom lens systemillustrating redirection of the radiation axis with different positionsof the zoom lens group and surface shapes between the liquids to producedifferent focal lengths and focus distances.

DETAILED DESCRIPTION

In the following description of preferred embodiments, reference is madeto the accompanying drawings that form a part hereof, and in which isshown by way of illustration specific embodiments in which the inventionmay be practiced. It is to be understood that other embodiments may beutilized and structural changes may be made without departing from thescope of the invention.

U.S. Provisional Patent Application No. 60/783,338 filed on Oct. 8, 2007and titled “Liquid Optics Zoom Lens and Imaging Apparatus,” hereinincorporated by reference in its entirety, discloses a zoom lens systemthat employs liquid optics to provide zoom and focus functionality. Theuse of liquid optics for zooming and focusing provides for alternativelens configurations with redirection of the radiation axis. An exemplaryzoom lens system employing liquid optics to provide zoom and focusfunctionality is described first, followed by embodiments employingredirection of the radiation axis.

Liquid Optics In a Zoom Lens System

FIG. 1 illustrates a block diagram of a camera 100 with a zoom lens 102.A zoom lens is an assembly of lens elements with the ability to varyfocal length. The individual lens elements may be fixed in place, orslide axially along the body of the lens. A lens group may consist ofone or more lens elements. At least one movable lens group providesvariation of the magnification of an object. As the at least one lensgroup moves to accomplish magnification, the position of the focal planemay also move. At least one other movable lens group may move tocompensate for the movement of the focal plane to maintain a constantfocal plane position. Compensation for the movement of the focal planemay also be achieved mechanically by moving the complete lens assemblyas the magnification of the lens changes.

The individual lens elements may be constructed from solid-phasematerials, such as glass, plastic, crystalline, or semiconductormaterials, or they may be constructed using liquid or gaseous materialssuch as water or oil. The space between lens elements could contain oneor more gases. For example normal air, nitrogen or helium could be used.Alternatively the space between the lens elements could be a vacuum.When “Air” is used in this disclosure, it is to be understood that it isused in a broad sense and may include one or more gases, or a vacuum.

A zoom lens will often have three or more moving lens groups to achievethe zoom and focusing functions. A mechanical cam may link two movablelens groups to perform zooming, and a third movable lens group may beused for focus.

The zoom range is determined in part by the range of movement for themovable lens elements. Greater zoom ranges require additional space formovement of the lens elements. One or more of the movable lens groupsmay be replaced by a lens group that implements liquid cell technology.Because liquid cells do not require space for axial movement, the lengthof the lens design which contains the movable lens groups may bereduced. Alternatively, the space that would have been used for axialmovement of the movable lens groups can be used to include additionaloptical elements or folds. Although a liquid cell does not require spacefor movement, it may be part of a movable lens group.

A liquid cell may be used for both zooming and focusing. In oneembodiment, a movable lens group is used with a lens group thatimplements liquid cell technology. There is no need for a mechanical camwith one movable lens group. Not having a cam allows for additionalmovements.

One or more movable lens groups are used with one or more liquid cellsto achieve zooming and focusing. A single movable lens group and asingle liquid cell can perform both zooming, focusing and compensationfor thermal effects. In one implementation, a zoom system has at least afirst and second lens group. The first lens group is relatively highpower, and the second lens group is relatively low power, the lens powerbeing equivalent to the inverse of the focal length of the lens. Thefirst lens group comprises conventional glass or other solid lenses andthe second lens group comprises at least one liquid lens.

A liquid cell uses two or more liquids to form a lens. The focal lengthof the lens is partly determined by the angle of contact between theliquids and the difference in the refractive index of the liquids. Therange of power variation is limited by the difference in the refractiveindex of the liquids employed and the finite range of radius ofcurvature at the surface interface between the liquids due to spaceconstraints. U.S. Patent Application Publication No. 2006/0126190,herein incorporated by reference, discloses a lens employing thedeformation of a drop of liquid through electrowetting.

Presently contemplated liquid lens systems will have a difference inrefractive index of at least about 0.2, preferably at least about 0.3,and in some embodiments at least about 0.4. Water has a refractive indexof about 1.3, and adding salt may allow varying the refractive index toabout 1.48. Suitable optical oils may have a refractive index of atleast about 1.5. Even by utilizing liquids with higher, lower or higherand lower refractive indices, for example a higher refractive index oil,the range of power variation remains limited. This limited range ofpower variation usually provides less magnification change than that ofa movable lens group. Therefore, in a simple zoom lens system, toprovide zooming while maintaining a constant image plane position mostof the magnification change may be provided by one movable lens groupand most of the compensation of defocus at the image plane during themagnification change may be provided by one liquid cell. However, itshould be noted that more movable lens groups or more liquid cells, orboth, may be utilized.

The movable lens group can have a positive or negative power. The liquidcell can have a range of variable power where the power is alwayspositive, always negative or goes from positive to negative, or viceversa. Proper arrangement of the movable lens group and the liquid cellprovides an extended zoom ratio of greater than 2× and preferablygreater than 3× while offering good image quality throughout the zoomrange. The arrangement, in addition to zooming, may also providefocusing at different object distances over an extended focus range byutilizing additional available power variation from the liquid cell, themovable lens group or both. This additional power variation provided bythe liquid cell or the movable lens group or both for focusing isreadily available. Since one movable lens group does not necessarilyrequire a cam with a fixed locus of movement, the position of themovable zoom lens group can be adjusted for zooming and focusing. Highperformance imaging is achieved by utilizing both the movable zoom lensgroup and the liquid cell for zooming and focusing.

It is also possible to replace the movable zoom lens group with at leastone liquid cell. This would increase the complexity of the opticalsystem and may cause the optical system to have other disadvantages,such as reduced magnification change.

FIG. 1 also illustrates a lens control module 104 that controls themovement and operation of the lens groups in lens 102. The controlmodule 104 includes electronic circuitry that controls the radius ofcurvature in the liquid lens cell. Electronic circuitry may also controlthe position of the movable lens group. The appropriate electronicsignal levels for various focus positions and zoom positions can bedetermined in advance and placed in a lookup table. Alternatively,analog circuitry or a combination of circuitry and a lookup table cangenerate the appropriate signal levels. In one embodiment, a polynomialis used to determine the appropriate electronic signal levels. Pointsalong the polynomial could be stored in a lookup table or the polynomialcould be implemented with circuitry.

Thermal effects may also be considered in the control of the radius ofcurvature of surface between the liquids or the position of movable lensgroups or both. The polynomial or lookup table may include an additionalvariable related to the thermal effects.

The control module 104 may include preset controls for specific zoomsettings or focal lengths. These settings may be stored by the user orcamera manufacturer.

FIG. 1 further illustrates an image capture module 106 that receives anoptical image corresponding to an external object. The image istransmitted along an optical axis through the lens 102 to the imagecapture module 106. The image capture module 106 may use a variety offormats, such as film (e.g., film stock or still picture film), orelectronic image detection technology (e.g., a CCD array, CMOS device orvideo pickup circuit). The optical axis may be linear, or it may includefolds or other redirection of the radiation axis. It should beunderstood that a fold as used herein is intended to be interpretedbroadly. A variety of optical elements are available that redirect theradiation axis, and the scope of the invention should not be limited toa specific type of optical element.

Image storage module 108 maintains the captured image in, for example,on-board memory or on film, tape or disk. In one embodiment, the storagemedium is removable (e.g., flash memory, film canister, tape cartridgeor disk).

Image transfer module 110 provides transferring of the captured image toother devices. For example, the image transfer module 110 may use one ora variety of connections such as a USB port, IEEE 1394 multimediaconnection, Ethernet port, Bluetooth wireless connection, IEEE 802.11wireless connection, video component connection, or S-Video connection.

The camera 100 may be implemented in a variety of ways, such as a videocamera, a cell phone camera, a digital photographic camera, or a filmcamera.

An embodiment of a zoom lens will now be described by way of a designexample. Referring first to FIG. 2, each lens element is identified bythe letter “E” followed by a numeral from 1 through 20 and the generalconfiguration of each lens element is depicted, but the actual radius ofeach lens surface is set forth below in TABLE 1. The lens, object, stopor iris and image surfaces are identified by a numeral from 1 through36. The three lens groups are identified in FIG. 2 by the letter “G”followed by a numeral from 1 through 3 and the liquid lens cell isidentified by the letters “LC” and comprises optical surfaces 19 through23. The optical axis is identified in FIG. 2 by a numeral 38.

Each lens element has its opposite surfaces identified by a separate butconsecutive surface number as, for example, lens element E1 has lenssurfaces 2 and 3, lens element E9 has lens surfaces 17 and 18 and soforth, as shown in FIG. 2. The location of the object to be imaged,particularly as it relates to focus distance, is identified by avertical line and the numeral 1 on the optical axis 38 and the realimage surface is identified by the numeral 36. All of the lens surfacesare spherical or plano except lens surfaces 4 and 8 which are asphericsurfaces that are non-spherical, non-plano but rotationally symmetricalabout the optical axis.

Before describing the detailed characteristics of the lens elements, abroad description of the lens groups and their axial positions andmovement, and, the liquid lens cell and the variation in surface shapeof contacting liquids will be given for the zoom lens system 60.

The positive or negative power of each lens group is defined as theinverse of the focal length. The resultant optical power of each groupof lenses is as follows: the objective lens group G1 is positive, thezoom lens group G2 is negative and the rear lens group G3 is positive,from a lower positive value to a higher positive value as the shape ofthe surface in the liquid cell is varied. The horizontal arrow witharrowheads on both ends in the upper portion of FIG. 2 indicates thatthe zoom lens group G2 is movable in both axial directions.

While only the lens elements are physically shown in FIG. 2, it is to beunderstood that mechanical devices and mechanisms are provided forsupporting the lens elements and for causing axial movement of themovable zoom lens group in a lens housing or barrel. In addition, it isto be understood that electronic circuitry changes the profile of thevariably shaped optical surface in the liquid lens cell.

The lens construction and fabrication data for the above described zoomlens system 60 is set forth below in TABLE 1. The data in TABLE 1 isgiven at a temperature of 25° C. (77° F.) and standard atmosphericpressure (760 mm Hg). Throughout this specification measurements are inmillimeters (mm) with the exception of wavelengths which are innanometers (nm). In TABLE 1, the first column “Item” identifies eachoptical element and each location, i.e. object plane, image plane, etc.,with the same numeral or label as used in FIG. 2. The second columnidentifies the “Group” to which that optical element (lens) belongs withthe same numerals used in FIG. 2. The third column “Surface” is a listof the surface numbers of the object (line “1” in FIG. 2 and “Object” inTABLE 1), the Stop (iris) 13 and each of the actual surfaces of thelenses, as identified in FIG. 2. The fourth column “Focus Position”identifies three typical focus positions (F1, F2 and F3) for the zoomlens system 60 wherein there are changes in the distance (separation)between some of the surfaces listed in the third column and there arechanges in the radius of curvature of the surface 21 listed in the thirdcolumn, as described below more thoroughly. The fifth column“Separation” is the axial distance between that surface (third column)and the next surface. For example, the distance between surface S2 andsurface S3 is 1.725 mm.

The sixth column, headed by the legend “Radius of Curvature,” is a listof the optical surface radius of curvature for each surface, with aminus sign (−) meaning the center of the radius of curvature is to theleft of the surface, as viewed in FIG. 2 and “Infinity” meaning anoptically flat surface. The asterisk (*) for surfaces 4 and 8 indicatethese are aspheric surfaces for which the “radius of curvature” is abase radius. Use of aspherical surfaces provides for the correction ofaberrations in the zoom lens while enabling a smaller overall size and asimpler configuration. The formula and coefficients for the surfaceprofiles of aspheric surfaces 4 and 8 are governed by the followingequation:

$z = {\frac{{cy}^{2}}{1 + \left\lbrack {1 - {\left( {1 + \kappa} \right)c^{2}y^{2}}} \right\rbrack^{1/2}} + {Ay}^{4} + {By}^{6} + {Cy}^{8} + {Dy}^{10} + {Ey}^{12} + {Fy}^{14}}$

-   -   where:    -   c=surface curvature (c=1/r where r is the radius of curvature)    -   y=radial aperture height of surface measured from the X and Y        axis, where:        y=(X ² +Y ²)^(1/2)    -   κ=conic coefficient    -   A, B, C, D, E, F=4^(th), 6^(th), 8^(th), 10^(th), 12^(th) and        14^(th), respectively, order deformation coefficients    -   z=position of a surface profile for a given y value or measured        along the optical axis from the pole (i.e., axial vertex) of the        surface        The coefficients for surface 4 are:    -   κ=−0.6372    -   A=+0.9038×10⁻⁶    -   B=+0.2657×10⁻⁸    -   C=−0.1105×10⁻¹⁰    -   D=+0.4301×10⁻¹³    -   E=−0.8236×10⁻¹⁶    -   F=+0.6368×10⁻¹⁹        The coefficients for surface 8 are:    -   κ=+0.0000    -   A=+0.5886×10⁻⁴    -   B=−0.5899×10⁻⁶    -   C=+0.8635×10⁻⁸    -   D=−0.5189×10⁻¹⁰    -   E=−0.1186×10⁻¹¹    -   F=+0.1631×10⁻¹³

Columns seven through nine of TABLE 1 relate to the “Material” betweenthat surface (third column) and the next surface to the right in FIG. 2,with the column “Type” indicating whether there is a lens (Glass) orempty space (Air) or liquid lens (Liquid) between those two surfaces.The glass and liquid lenses are identified by optical glass or liquid inthe column “Code”. For convenience, all of the lens glass has beenselected from glass available from Ohara Corporation and the column“Name” lists the Ohara identification for each glass type, but it is tobe understood that any equivalent, similar or adequate glass may beused. Also, the lens liquid of oil has been selected from a liquidavailable from Cargille Laboratories, Inc., and water is commonlyavailable from various sources, but it is to be understood that anyequivalent, similar or adequate liquid may be used. The water liquid atsurface 20 has the following refractive indices 1.331152, 1.332987,1.334468 and 1.337129 at respective wavelengths 656.27, 589.29, 546.07and 486.13 nanometers. The oil liquid at surface 21 has the followingrefractive indices 1.511501, 1.515000, 1.518002 and 1.523796 atrespective wavelengths 656.27, 589.29, 546.07 and 486.13 nanometers.

The last column of TABLE 1 headed “Aperture Diameter” provides themaximum diameter for each surface through which the light rays pass. Allof the maximum aperture diameters, except for the Stop surface 13, aregiven at a wavelength of 546.1 nanometers for a maximum image diameterof about 6 mm and F-numbers of F/2.8 to F/4.0 at the Image Plane, forall Zoom and Focus Positions. The maximum aperture diameter of the Stopsurface 13 is given in TABLE 1 at a wavelength of 546.1 nanometers andan F-number of F/2.8 at the Image Plane for Zoom Position Z1 and FocusPosition F1. At the Image Plane 36, the Maximum Aperture Diameter isgiven as an approximate value.

TABLE 1 Optical Prescription Focus Radius of Material Aperture ItemGroup Surface Position Separation Curvature (mm) Type Name Code Diameter(mm) Object 1 F1 Infinity Infinity Air F2 1016.2500 F3 378.7500 E1 G1 2All 1.7250 59.1716 Glass SLAM66 801350 37.161 3 All 0.0750 34.5954 Air35.567 E2 G1 4 All 6.7565 *33.0488 Glass SFPL51 497816 35.618 5 All0.0750 2758.9929 Air 35.182 E3 G1 6 All 5.8657 32.7151 Glass SFPL53439950 33.680 7 F1 TABLE 2 −2981.4301 Air 33.034 F2 TABLE 2 F3 TABLE 2E4 G2 8 All 0.7652 *461.6464 Glass SLAH64 788474 14.273 9 All 3.83338.3339 Air 11.605 E5 G2 10 All 2.6582 −12.6370 Glass SFPL53 43995011.587 E6 G2 11 All 3.2165 18.1883 Glass SLAM66 801350 12.383 12 F1TABLE 3 −55.4718 Air 12.337 F2 TABLE 3 F3 TABLE 3 Stop/ G3 13 All 0.6371Infinity 6.708 Iris E7 G3 14 All 5.7168 −26.3844 Glass SLAH65 8044666.757 E8 G3 15 All 2.6250 9.3177 Glass STIH53 847238 8.304 16 All 0.8432−16.3366 Air 8.533 E9 G3 17 All 2.5647 −9.2859 Glass SLAH58 883408 8.50818 All 2.2767 −11.1961 Air 9.665 E10 G3 19 All 0.4500 Infinity GlassSBSL7 516641 10.151 E11 G3 20 All 1.5000 Infinity Liquid WATER 10.201E12 G3 21 F1 1.5000 TABLE 4 Liquid OIL T300 10.367 04091- AB F2 TABLE 4F3 TABLE 4 E13 G3 22 All 0.4500 Infinity Glass SBSL7 516641 10.584 23All 0.0750 Infinity Air 10.642 E14 G3 24 All 3.1583 120.2680 GlassSLAH65 804466 10.680 E15 G3 25 All 0.6000 −7.2241 Glass STIH10 72828510.724 26 All 0.0750 13.8153 Air 10.634 E16 G3 27 All 3.0844 13.7118Glass SBSM10 623570 10.696 28 All 0.3424 −11.1618 Air 10.713 E17 G3 29All 0.6000 −9.5071 Glass STIH13 741278 10.652 30 All 0.0750 68.8748 Air11.180 E18 G3 31 All 1.7063 18.2078 Glass SLAL13 694532 11.589 32 All26.6908 −115.6915 Air 11.592 E19 G3 33 All 3.1085 10.2784 Glass SNPH1808228 9.888 E20 G3 34 All 2.7193 −9.9003 Glass SLAH58 883408 9.581 35All 2.6192 58.0014 Air 7.805 Image 36 All 0.0000 Infinity Air 6.008

Zoom lens system 60 is provided with an optical stop at the surface 13which controls the diameter of the aperture through which light rays maypass at that point. The optical stop is the location at which a physicaliris (or diaphragm) is located. The iris is located before the rear lensgroup G3 and is axially stationary with that lens group. Note that inFIG. 4A, the rim rays pass through the axis side of the tic marks of theoptical stop surface 13 such that the zoom lens system has no vignettingof light beams at any field position, zoom position and focus position.However, note that the F-number varies through zoom and focus positionsand the iris opens or closes accordingly. The diameter of the iris atzoom positions Z1-Z8 for focus position F1 is 6.71, 6.39, 5.96, 5.53,5.18, 4.84, 4.63 and 4.61. This shows that the iris located at 13 shouldclose as the focal length increases. As compared to focus position F1,the diameter of the iris at zoom positions Z1-Z8 for focus positions F2and F3 changes by a small amount of less than 0.3 mm diameter tomaintain the same F-numbers as for focus position F1.

Referring to TABLE 1, for illustrating the scope and versatility of thedesign there are eight different Zoom Positions Z1, Z2, Z3, Z4, Z5, Z6,Z7 and Z8 and three different Focus Positions F1, F2 and F3 set forth inthe data which, in effect, provides specific data for twenty four(8×3=24) different combinations of positions for the movable zoom lensgroup G2 and the variable shape optical surface 21.

The focal lengths of zoom lens system 60 for zoom positions Z1-Z8 atfocus position F1, at a wavelength of 546.1 nanometers are; 5.89, 7.50,11.25, 15.00, 18.75, 30.00, 41.25 and 45.00 mm, respectively. Thecorresponding F-numbers for the focal lengths for data positions Z1-Z8,at a wavelength of 546.1 nanometers are; 2.80, 2.90, 3.05, 3.25, 3.45,3.70, 3.95 and 4.00, respectively.

For Focus Position F1 the Object Plane 1 is assumed to be at infinity,for F2 the Object Plane 1 is at an intermediate distance of about1016.25 mm, and for F3 the Object Plane 1 is at a close distance ofabout 378.75 mm (i.e., 378.75 mm away from the image plane). At each ofthese three Focus Positions F1, F2 and F3, the lens groups G1 and G3remain in the same position throughout the full range of movement of thezoom lens group G2. TABLES 2 and 3 provide separation values of surfaces7 and 12 and TABLE 4 provides the radii of curvature of surface 21 forzoom positions Z1-Z8 and F1-F3.

TABLE 2 Separation Values for Surface 7 Surface Focus Z1 Z2 Z3 Z4 Z5 Z6Z7 Z8 7 F1 0.0832 5.7132 13.7126 18.4633 21.6974 27.4007 30.5400 31.30967 F2 0.0902 5.7486 13.6468 18.3289 21.5154 27.0776 30.0174 30.7361 7 F30.0750 5.6942 13.4674 18.1217 21.3355 26.7467 29.5798 30.2701

TABLE 3 Separation Values for Surface 12 Surface Focus Z1 Z2 Z3 Z4 Z5 Z6Z7 Z8 12 F1 31.5294 25.8992 17.8996 13.1486 9.9140 4.2101 1.0701 0.300012 F2 31.5178 25.8581 17.9590 13.2762 10.0892 4.5268 1.5870 0.8729 12 F331.5324 25.9120 18.1380 13.4831 10.2689 4.8577 2.0248 1.3384

TABLE 4 Radii of Curvature for Surface 21 Surface Focus Z1 Z2 Z3 Z4 Z5Z6 Z7 Z8 21 F1 −33.9902 −40.9700 −60.9667 −84.8892 −106.7630 −101.7297−58.3998 −48.6792 21 F2 −34.3890 −42.0587 −65.5384 −101.1799 −154.9184−370.2777 −263.5374 −212.3139 21 F3 −35.0134 −43.6001 −72.6330 −133.7178−351.2333 214.4454 125.5481 115.8049

It will be understood that continuous focusing is available between theextreme Focus Positions F1 and F3, that continuous zooming is availablebetween the extreme Zoom Positions Z1 and Z8, and that any combinationof continuous focusing and zooming is available within the describedfocus and zoom ranges with the lens system 60.

The zoom lens system 60 shown in FIG. 2 and prescribed in TABLE 1 hasfocal lengths for lens groups G1 and G2 of 54.30 and −12.25 mmrespectively. Also, lens group G3, due to the variable shape of theoptical surface 21 between the liquids, has a variable focal lengthwhich has a minimum value of +30.18 mm and a maximum value of +38.97 mmat zoom position Z1 and focus position F1, and, zoom position Z8 andfocus position F3 respectively. The liquid cell LC of zoom lens system60 is shown in FIGS. 3A and 3B, demonstrating the two extreme radii ofcurvature from TABLE 1 of the variable shape optical surface 21 betweenthe liquids. In FIGS. 3A and 3B the two radii of curvature of surface 21are about −33.99 and +115.80 mm respectively. The two extreme focallengths of the liquid cell LC, in FIGS. 3A and 3B, are −185.20 and630.97 mm respectively. This difference happens at zoom position Z1 andfocus position F1, and, zoom position Z8 and focus position F3. In thisembodiment the volume of the two liquids between surfaces 20, 21 and 21,22 varies as the shape of the variable surface changes. However, it isalso possible to maintain a constant volume for each liquid by applyingsmall, equal but opposite, changes to the axial separation betweensurfaces 20, 21 and 21, 22.

Referring now to FIGS. 4A, 4B, and 4C, the zoom lens system 60 is shownwith the zoom lens group in various positions, the shape of the variablesurface in the liquid cell in various positions and with light raytraces for those positions. FIG. 4A represents the focus position F1 andzoom position Z1 for which data is set forth above in TABLE 1 withinfinity focus and a small focal length of about 5.9 mm. FIG. 4Brepresents the focus position F2 and zoom position Z3 from TABLE 1 withan intermediate focus and a focal length of about 11.3 mm. FIG. 4Crepresents the focus position F3 and zoom position Z8 from TABLE 1 withclose focus and a focal length of about 44.8 mm.

FIGS. 4A, 4B and 4C show three axial locations of the zoom lens group G2with corresponding three surface shapes for the variable optical surface21 for the respective zoom and focus positions; Z1, F1 and Z3, F2 andZ8, F3.

The optical performance of zoom lens system 60 is given in FIGS. 5A, 5Band 5C wherein the diffraction based polychromatic modulation transferfunction (“MTF”) data (modulation versus spatial frequency) is shown inpercent (%) for five different Field Positions in three differentcombinations of the zoom and focus positions set forth in TABLE 1,namely (Z1, F1), (Z3, F2) and (Z8, F3) which are representativeexamples. The Field Positions are set forth in two values, both thenormalized image height (mm) and the actual object space angle (degree)from the optical axis. The MTF percentages are at the wavelengths andweightings set forth in the top right-hand corner of FIGS. 5A, 5B and 5Cand are graphically shown for tangential (T) and radial (R) directionsof measurement at the image plane 36. Note that the tangential andradial values are equal at the axial field position (AXIS) and aredepicted with only one plot. The maximum spatial frequency shown is 90cycles/mm which given the image diameter of about 6 mm and choice ofdetector pixel size may provide high quality images at least up to highdefinition television (HDTV) resolution, namely 1920 pixels horizontallyby 1080 pixels vertically. MTF at a spatial frequency is a relativelystandard measurement of optical performance, wherein the value “90cycles/mm” means 90 pairs of black and white lines per millimeter on achart from which the clarity is determined. The highest MTF value isabout 89% at the full radial field for zoom position Z1 and focusposition F2. The lowest MTF value is about 58% at the full tangentialfield for zoom position Z8 and focus position F3. The minimum relativeillumination is about 75% at zoom position Z1 and focus position F1. Ingeneral, higher relative illumination values are better, because a lownumber means that light is falling off in the corners of the picture.High full field relative illumination is preferred for state of the artdetectors, which have a constant response to light in all areas and willfaithfully reproduce shading in the corners of the image along withchanges to the image during zooming. Illumination less than 50% mayresult in shading in an electronic detector, but will likely beacceptable for film. The highest positive distortion is +3.04% at zoomposition Z3 and focus position F1 and the lowest negative distortion is−2.98% at zoom position Z1 and focus position F3. The so-called“breathing” problem of lenses in general (but which may be moreprevalent in zoom lenses) wherein the image changes size from far toclose focus is virtually absent in zoom lens system 60 at the shortfocal length of the zoom range where it is most noticeable due to thelarge depth of field. The lowest breathing is −0.2% at zoom position Z1and focus position F3 and the highest breathing is −19.5% at zoomposition Z8 and focus position F3. Breathing is the percentage change inmaximum field angle from infinity focus to a selected focus.Accordingly, at infinity focus (F1), breathing is zero because that isthe reference field of view.

All of the performance data is given at a temperature of 25° C. (77°F.), standard atmospheric pressure (760 mm Hg), and at the fullapertures available in the zoom lens system 60. However, the zoom lenssystem 60 does provide substantially constant performance, as forexample the MTF values, over a temperature range of 0° to 40° C. (32° to104° F.) and, if a small degradation in performance (MTF) is acceptable,the operable temperature range can be extended to −10° to 50° C. (14° to122° F.) or more. For a change temperature the optimum performance maybe achieved by further axial adjustment of the zoom lens group G2 orfurther change of shape of the contacting optical surface 21 or acombination of both together. This may happen at all zoom and focuspositions. At low temperatures of about 0° C. (32° F.) or below, toavoid freezing (forming a solid), the liquids may need to be heated orbe replaced with doped liquids in a similar way to anti-freeze beingadded to water in a car radiator for low temperature operation. However,note that these material temperature changes preferably should notsignificantly change the optical characteristics of the liquids.

While the described embodiment using zoom lens system 60 is of theappropriate dimensions for use with a 6 mm diameter (so called thirdinch chip sensor), the dimensions of this zoom lens system may beappropriately scaled up or down for use with various film and electronicdetector image formats.

Liquid lens cells may have a limited clear aperture diameter. If asufficiently small detector is used, the liquid lens cell may be locatednear the detector. Alternatively, the liquid lens cell may be locatednear an intermediate image where the light beam “waist” is sufficientlynarrow. The liquid lens cell could be placed before the intermediateimage, after the intermediate image, or liquid lens cells could beplaced both before and after the intermediate image. The waist effectcan happen near the stop or the iris. As shown in Table 2, the diameterat the iris is approximately 6.7 mm. Because of the small diameter atthe stop or iris, it may be appropriate to place a liquid lens cell inthe vicinity of the stop or iris.

Among the many advantages of the zoom lens system 60 is that ofproviding zooming over a wide range of focal lengths utilizing only oneaxially moving zoom lens group. The design of the zoom lens system 60creates a high performance and mechanically less complex lens systemthan most conventional high performance zoom lens systems which requireat least two axially movable zoom lens groups and correspondingmechanics. The unique lens design of the zoom lens system 60 providesfocusing over a large region of focus distance without additionalmovable lens groups and corresponding mechanics. The disclosed design ofzoom lens system 60 is exemplary, and other designs will fall within thescope of the invention. Other features and advantages of the zoom lenssystem 60 will appear to those skilled in the art from the foregoingdescription and the accompanying drawings.

Liquid Optics and Redirection of the Radiation Axis in a Zoom LensSystem

Using liquid lens cells to replace one or more moving lens groupsresults in additional configuration options for the optical path.Replacing moving lens groups with liquid lens cells results in a morecompact system. However, a linear optical design may result in a lensthat is longer than desired. The use of liquid lens cells instead of amoving group facilitates the use of optical elements such as folds toredirect of the radiation axis reduce the physical length of a lens.Although the overall length of the optical path through the lens mayremain the same, the liquid lens cells provide strategic space forfolding that reduces the length in one or more directions. This allowslonger overall lens lengths to be used in smaller camera packages. Forexample, many point and shoot cameras and cell phone cameras do not havelarge amounts of space for a long lens. Using liquid cells incombination with folds allows for better lens systems in these smallcamera packages. Larger cameras can also benefit from reducing thecamera package length that would be required for a lens system that didnot use folds.

FIG. 6 shows an optical diagram of a zoom lens system employing liquidsand a single fold 41. The use of liquids instead of movable lens groupsreduces the space requirements and provides additional options forstrategic placement of airspaces for fold mirrors or prisms. This figureshows placement of folds where they will not interfere with moving lensgroups.

Overall length of zoom lens system 60 may be reduced with somedegradation in performance unless increased optical complexity such asmore lens elements and/or aspherical surfaces are introduced. However, areduced length may be achieved by folding of the zoom lens system. FIG.6 shows a single 45 degree fold 41 in the large airspace in the rearlens group G3, to redirect the radiation path by 90 degrees.

FIG. 7 is an optical diagram of a zoom lens system employing liquids anda dual fold. FIG. 7 shows dual 45 degree folds 42 and 43 in the largeairspace in the rear lens group G3, to redirect the radiation path twotimes by a total of 180 degrees so that the radiation has reverseddirection. This arrangement may be preferred for packaging of the zoomlens system 60 in a camera box. Also, the zoom lens system may have aconstant aperture of F/2.8 through all zoom and focus positions but tomaintain about the same zoom lens system diameter, some vignetting mayoccur. In this case, some degradation of image quality may appear butmay be partially corrected by re-optimization of the prescription of thezoom lens system. The zoom lens system may be arranged so thatvignetting does not occur.

FIGS. 8A and 8B are optical diagrams of a zoom lens system illustratingredirection of the radiation axis with different positions of the zoomlens group and surface shapes between the liquids. This embodiment isillustrative of an alternative lens layout. FIG. 8A illustrates a zoomposition that enlarges the image to a point that the optic traces exceedparameters of the lens system. This embodiment is illustrative of onedesign option, and minor changes could be made to the design to correctthis effect.

Folds 44 and 45 are substantially parallel, so that light rays leavinglens elements 50 are substantially parallel to light rays entering thelens system through lens 46. Lens group 47 remains fixed, while lensgroup 48 moves to substantially provide zooming. Lens group 49 comprisesa liquid lens cell that performs zooming and focusing functions.

FIGS. 9A, 9B and 9C are optical diagrams of a zoom lens system where theliquid lens cells and folds have been strategically placed toadvantageously shorten the length of the lens system. Light enters thelens system through lens group 200. Lens group 201 moves tosubstantially provide zooming. The light rays pass through the iris orstop 202 and enter lens group 203 comprising a liquid lens cell. Fold204 directs the light through lens group 205, which comprises a liquidlens cell having a variable surface 206. The light rays then passthrough lens group 207. Fold 208 redirects the light rays through lensgroup 209 and towards an image plane 210. FIG. 9A illustrates a focallength of approximately 6 mm, F/2.8, and infinity focus. FIG. 9Billustrates a focal length of approximately 15 mm, F/2.8, and infinityfocus. FIG. 9C illustrates a focal length of approximately 51 mm, F/2.8and infinity focus.

The first liquid lens cell in lens group 203 has a largest clearaperture diameter of approximately 10 mm. The second liquid lens cell inlens group 205 has a largest clear aperture diameter of approximately 16mm. By including a camera flash to slow down the taking aperture at ornear the long focal length, it may be possible to revert to one liquidlens cell.

It is to be noted that various changes and modifications will becomeapparent to those skilled in the art. Such changes and modifications areto be understood as being included within the scope of the invention asdefined by the appended claims.

What is claimed is:
 1. A zoom lens system having a zoom range andconfigured to collect radiation emanating from an object side space ofthe zoom lens system and deliver the radiation to an image side space,the zoom lens system comprising: an objective lens group configured tobe axially stationary and positively powered; a zoom lens grouppositioned on an image side of the objective lens group and continuouslymovable along an optical axis over the entire zoom range; an axiallystationary lens group aligned along the optical axis and positioned onan image side of the zoom lens group, the axially stationary lens groupcomprising at least one liquid lens cell, the liquid lens cellcomprising a first liquid in contact with a second liquid to form anoptical surface having a variable shape between the contacting liquids;an axially stationary optical stop positioned along the optical axisbetween the zoom lens group and the axially stationary lens group, theoptical stop having an iris configured to change a size of its diameter;and an optical redirection element aligned to form a fold along theoptical axis, wherein the objective lens group, the axially stationarylens group, the zoom lens group, and the optical redirection elementcollect radiation emanating from the object side space of the zoom lenssystem and deliver the radiation to the image side space without formingan intermediate image along the folded optical axis, wherein theobjective lens group, the zoom lens group, the optical stop, and theaxially stationary lens group are positioned along the optical axisbefore the optical redirection element, wherein a zoom ratio of the zoomlens system is greater than 3×.
 2. The zoom lens system of claim 1,wherein the zoom lens system comprises a single axially movable zoomlens group.
 3. The zoom lens system of claim 1, wherein the axiallymovable zoom lens group does not include a liquid lens cell.
 4. The zoomlens system of claim 1, wherein the optical redirection elementcomprises a mirror.
 5. The zoom lens system of claim 1, wherein theoptical redirection element comprises a prism.
 6. The zoom lens systemof claim 1, wherein the optical redirection element reduces the physicallength of the zoom lens system.
 7. The zoom lens system of claim 1,wherein the liquid lens cell is located between the axially movable zoomlens group and the image side space on the common optical axis.
 8. Thezoom lens system of claim 1, further comprising a control modulecomprising electronic circuitry configured to control the shape of thecontacting optical surface and a position of the zoom lens group on theoptical axis.
 9. The zoom lens system of claim 8, wherein a lookup tableprovides a first index value corresponding to a focal setting and asecond index value corresponding to a zoom setting to the control moduleto electronically control the shape of the contacting optical surfaceand a position of the zoom lens group on the optical axis.
 10. The zoomlens system of claim 1, wherein the diameter of the iris is configuredto decrease with an increase in a focal length of the zoom lens system.11. The zoom lens system of claim 1, wherein the zoom ratio is at least7×.
 12. The zoom lens system of claim 1, wherein the zoom ratio is lessthan 8.5×.
 13. A camera system comprising: a zoom lens comprising, inorder along a common optical path from an object side of the zoom lensto an image side of the zoom lens, an axially stationary objective lenshaving a positive optical power, a movable lens group, an axiallystationary optical stop having an iris with a variable diameter, aliquid cell lens group and an optical redirection element, the objectivelens group, the movable lens group, the liquid cell lens group, theoptical stop, and the optical redirection element aligned on the commonoptical path, wherein the movable lens group is continuously movablealong the optical path over an entire zoom range and the opticalredirection element redirects the radiation axis to form a fold in theoptical path; and an image capture element positioned at a focallocation on the image side of the zoom lens, wherein the zoom lenssystem does not form an intermediate image in the folded optical path,wherein a zoom ratio of the zoom lens is greater than 3×.
 14. The camerasystem of claim 13, wherein the zoom lens comprises a single movablelens group.
 15. The camera system of claim 13, wherein the image captureelement is a CCD detector.
 16. The camera system of claim 13, whereinthe image capture element is film.
 17. The camera system of claim 13,wherein the image capture element is a CMOS detector.
 18. The camerasystem of claim 13, further comprising a control module comprisingelectronic circuitry configured to control an optical power of theliquid cell lens group and a position of the zoom lens group along theoptical path.
 19. The camera system of claim 18, wherein a lookup tableprovides a first index value corresponding to a focal setting and asecond index value corresponding to a zoom setting to the control moduleto electronically control the optical power of the liquid cell lensgroup and the position of the movable lens group along the optical path.20. The camera system of claim 13, wherein the diameter of the iris isconfigured to decrease with an increase in a focal length of the zoomlens.
 21. The camera system of claim 13, wherein the zoom ratio is atleast 7×.
 22. The camera system of claim 13, wherein the zoom ratio isless than 8.5×.